The properties of polycrystalline manganese ferrite thin films have been discussed in previous papers. The present study was undertaken to obtain supplementary information on the magnetic anisotropy and domain properties of the films. The ferrite films were grown epitaxially by an evaporation process. An advantage of working with single-crystalline ferrite films is that studies of the domain structure are simplified. Furthermore, the magnetic anisotropy is not reduced to the average of the randomly oriented crystallites. Epitaxial growth occurs on solids with equal or related crystal structures and types of chemical bonding, having at least one crystal face of comparable structure. Well-known substrates for spinel ferrites are MgO for many orientations and sapphire (Al2O3) with its (001) face fitting the (111) face of the spinel. In the present investigation monocrystalline MgO, with a lattice parameter of 4.21 A, was chosen as substrate. For manganese ferrite of ideal stoichiometry lattice parameters up to 8.50 A have been found. For the ferrite investigated, however, the fit between the lattices was not so exact. This meant that the misfit led to a compressive force in the ferrite lattice. The compression, however, was partly compensated by the occurrence of dislocations. In the special combination of MnFe204 and MgO the coefficients of thermal expansion are practically equal (12 x 10-6 mm °C-1), so that during cooling after the evaporation process little or no change in strain occurs. The strain introduced by the misfit is therefore the main source of influence, through magnetostriction, on the magnetic anisotropy.